<div class="btn">Confirm</div>

<!-- 背景色渐变原理，使用backgournd-position或者background-size进行放大或者移动 -->
<style>
  .btn {
    margin: 50px auto;
    width: 200px;
    line-height: 64px;
    text-align: center;
    color: #fff;
    font-size: 24px;
    cursor: pointer;
    background: linear-gradient(#024e8a 0%, #2d80c1 50%, #83c7fd 100%);
    background-size: 100% 150%;
    /* position 0 0 就是把背景图放置到容器的左上角，center是背景图放置到中间 */
    background-position: 0 0;
    transition: .3s;


  }

  .btn:hover {
    background-position: 0 75%;
  }
</style>